• Question: You work with particle accelerators, what do you think of the CERN laboratory in Switzerland’s recent announcement that neutrinos can travel faster than light?

    Asked by 02dawilliams to Peter, Ben on 16 Nov 2011.
    • Photo: Ben Still

      Ben Still answered on 15 Nov 2011:

      If it were true it would overturn our understanding of the Universe entirely – we would have to write the textbooks and the maths that describe Nature at its very largest and very smallest. But… my personal opinion, is that there is something unaccounted for in the error of the measurement. I work on an experiment extremely similar to the OPERA experiment that made the announcement and the errors quoted are really really small. As with everything in science only repeat measurements will determine if the result is correct or not – but sadly with neutrinos this will take some time, on the order of years.

      If you want to read and learn more of my opinion and other reasons why I don’t believe it to be true check out the following links:

      A seminar I gave (40mins): http://t.co/oW0zrfCU
      A series of blog posts on the results, starting here http://bit.ly/NuBlogFTL

    • Photo: Peter Williams

      Peter Williams answered on 16 Nov 2011:

      They’ve done exactly the right thing. They tried to find the discrepancy, but haven’t yet. So they’re asking the whole scientific community to check over their results. There are many things that could in principle explain the difference – remember this is only 20 nanoseconds, the time it takes light to travel about 7 meters – so equivalently a mistake in the distance between the source and detector of about that. For example, a mistake in the way GPS has been used to calculate that distance is being investigated. Another possible explaination is at the source – they monitor the current profile of a bunch of protons hitting a target, but this is not generating the neutrinos that fly from CERN to Gran Sasso, the target generates a whole bunch of stuff, some of which are things called pions, these decay to muons which in turn decay to neutrinos. So this is a pretty complicated chain of events – perhaps this process is not sufficiently understood.

      An independent experiment in the US called MINOS wll be performing their own test of the result later this year. So that’s one to watch.

      Also bear in mind that there are other effects that would happen if neutrinos are superluminal (faster than light) that have NOT been observed. Chiefly something called Cherenkov Radiation. This is like a sonic boom, but in light rather than sound. When we talk about the speed of light, we generally mean the speed of light in a vacuum. But light slows down in dense media – this is how lenses work. If a particle enters a material faster than the speed of light in that material then it quickly loses energy and emits light to get rid of that energy – called Cherenkov Radiaition after the guy that discovered it. Here is a picture of the spent nuclear fuel pool at La Hague in France (there is a smiliar one at Sellafield) http://s3.amazonaws.com/files.posterous.com/dougv/6VIfSDonKx0ywWTeXAeGmEcggy6pW4qdVvltla61Fgz5MfZ0PQdijxVNgmWU/spentfuelpool.jpg?AWSAccessKeyId=AKIAJFZAE65UYRT34AOQ&Expires=1321442343&Signature=7wH2fG2Ztt2rj3KP7I1BnxSmRPE%3D – this is a pool of water where they store spent reactor fuel, The rather pretty (or eerie if you are anti) blue glow is Cherenkov radiation. In this case the particles that is undergoing the sonic boom are neutrons, the speed of light in the water is slower than they are moving. But in principle the same would happen with neutrinos in the OPERA detector. But it doesn’t – so that’s inconsistant with their measurement of superluminal speeds.

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